Non-aqueous secondary batteries (hereinafter, also referred to simply as “secondary batteries”), such as lithium ion secondary batteries, have characteristics such as compact size, light weight, high energy-density, and the ability to be repeatedly charged and discharged, and are used in a wide range of applications. Consequently, in recent years, studies have been made to improve electrodes and other battery components with the aim of achieving even higher non-aqueous secondary battery performance.
An electrode for a secondary battery, such as a lithium ion secondary battery, normally includes a current collector and an electrode mixed material layer formed on the current collector. The electrode mixed material layer is formed, for example, by applying, onto the current collector, a slurry composition in which an electrode active material, a binder-containing binder composition, and so forth are dispersed in a dispersion medium, and drying the applied slurry composition.
In recent years, there have been attempts to improve binder compositions used in the formation of electrode mixed material layers in order to further improve secondary battery performance. In one specific example, it has been proposed that binding capacity between components (for example, an electrode active material) of an electrode mixed material layer and binding capacity between the electrode mixed material layer and a current collector (i.e., peel strength) can be increased, and secondary battery performance can be improved through use of a binder composition that contains two types of particulate polymers of differing particle diameters as a binder.
More specifically, PTL 1, for example, proposes that the peel strength of an electrode can be increased by using a binder obtained by mixing, in specific proportions, a particulate polymer for which the modal particle diameter of primary particles is at least 0.01 μm and less than 0.25 μm and a particulate polymer for which the modal particle diameter of primary particles is at least 0.25 μm and less than 3 μm.